Twelve passengers were hospitalised on Monday after a technical problem on a LATAM flight from Sydney to Auckland caused the Boeing-made plane to dip violently, the airline and first responders said.

At least one person was in serious condition after flight LA800 experienced an unspecified "technical event" over the Tasman Sea.

Passengers on the Boeing 787 Dreamliner told New Zealand media that the plane quickly lost altitude, flinging some towards the ceiling.

"People flew through the air because they weren't wearing their seatbelts" a passenger told public broadcaster RNZ.

"Some people got pretty injured. People were really scared as well," the unidentified man said, his voice shaking.

Brian Jokat, who was on board the flight, said he saw a passenger struck the roof of the plane before falling back down and hitting his ribs on an arm rest.

"He was on the roof of the plane on his back, looking down on me. It was like 'The Exorcist'," Jokat told RNZ, according to the NZ Herald.

A spokesperson for the Chile-based airline said "a technical event during the flight" had "caused a strong movement."

"The plane landed at Auckland Airport as scheduled," the airline said, adding it "deeply regrets any inconvenience and discomfort this situation may have caused."

US manufacturer Boeing has suffered a series of safety issues in recent years, including the fatal Lion Air and Ethiopian Airlines crashes of 737 Max planes in 2018 and 2019 that killed more than 350 people.

It was not immediately clear what caused the LATAM incident.

The passenger Jokat said that after the plane landed, the pilot came to the back of the cabin.

"I asked him 'what happened?' and he said to me 'I lost my instrumentation briefly and then it just came back all of a sudden'," Jokat said.

"I know he felt really bad for everyone."

"We are working to gather more information about the flight and will provide any support needed by our customer," Boeing said in a statement.

Gerard Campbell of the St John New Zealand ambulance service said medics were first made aware of the problem as the plane descended into New Zealand's largest city.

A phalanx of more than a dozen ambulances and other medical vehicles rushed to the scene to treat the wounded.

"Our ambulance crews assessed and treated approximately 50 patients, with one patient in a serious condition and the remainder in a moderate to minor condition," Campbell said.

"Twelve patients were transported to hospital," he said, after earlier putting the number at 13.

At least three of those treated were cabin crew.

Mobile phone footage posted by the NZ Herald showed concerned crew and passengers attending to one injured woman while flight attendants asked if there was a doctor aboard.

Data from airline tracker FlightAware showed the plane lost altitude about two hours into the three-hour flight.

Boeing is still reeling from a near-catastrophic incident in January when a fuselage panel on a Boeing 737 Max 9 Alaska Airlines jet blew off mid-flight. (AFP)